┬Y THE MIDDLE OF THE 19TH CENTURY ABOUT 70 ELEMENTS HAD BEEN CATALOGUED. ╬O FEATURE AMONG THESE ELEMENTS HAD BEEN FOUND, NOT UNTIL ─MITRI ═ENDELEEV ORGANIZED THE ELEMENTS IN COLUMNS ACCORDING TO ATOMIC MASS. ╚E NOTICED TRENDS AMONG THE ELEMENTS AND THEN CHANGED THE TABLE TO CONFORM WITH HIS FINDINGS. ╚E ARRANGED THE TABLE INTO COLUMNS SO THAT ELEMENTS IN A TREND WERE SIDE BY SIDE. ═ENDELEEV THUS CONSTRUCTED THE FIRST TRUE PERIODIC TABLE. ╘HE TABLE WAS RIDDLED WITH HOLES BECAUSE THERE WERE NOT ENOUGH ELEMENTS KNOWN AT THE TIME TO FILL THE GAPS. ╞ROM THE MISSING ELEMENTS, HE WAS ABLE TO PREDICT WITH GREAT ACCURACY THEIR CHEMICAL AND PHYSICAL PROPERTIES HE KNEW FROM THE OTHER SIMILAR ELEMENTS IN THE TRENDS. ┼VENTUALLY THEY WERE DISCOVERED AND DID INDEED MATCH HIS PREDICTIONS.
╘HE ═ODERN ╨ERIODIC ╘ABLE
╘HE MOST COMMONLY USED ╨ERIODIC ╘ABLE IS THE LONG FORM, WHICH HAS BEEN REPRODUCED IN THE GEO╨AINT FILES. ╘HE KEY CAN BE USED TO IDENTIFY THE PARTS OF THE TABLE, IF YOU ARE UNFAMILIAR WITH THE LAYOUT, OR AREE UNABLE TO DECIPHER THESE FROM SIGHT.
╘HE HORIZONTAL ROWS ARE CALLED PERIODS. ╘HERE ARE SEVEN PERIODS ON THE TABLE. ╘HE VERTICAL COLUMNS ARE CALLED GROUPS OR FAMILIES. ┼ACH GROUP IS IDENTIFIED BY A LETTER AND A NUMBER. ╟ROUPS 1A-7A AND 0 MAKE UP WHAT ARE CALLED THE REPRESENTATIVE ELEMENTS WHICH EXHIBT A VARIETY OF PROPERTIES. ╘HE ELEMENTS IN ANY GROUP HAVE THE SAME CHEMICAL AND PHYSICAL PROPERTIES. ╘HE PROPERTIES IN PERIODS, HOWEVER, CHANGE FROM GROUP TO GROUP. ╘HIS GIVES RISE TO THE PERIODIC LAW: ╫HEN ELEMENTS ARE ARRANGED IN ORDER OF INCREASING ATOMIC NUMBER, THERE IS A PERIODIC PATTERN IN THEIR PHYSICAL AND CHEMICAL PROPERTIES.
┼LEMENTS ARE CLASSIFIED FOUR DIFFERENT WAYS ACCORDING TO THEIR ELECTRON CONFIGURATION.
1. ╘HE NOBEL GASES. ╘HESE ARE ELEMENTS WHOSE OUTER S AND P SUBLEVELS ARE FILLED. ╘HIS IS GROUP 0 OF THE TABLE.
2. ╘HE REPRESENTATIVE ELEMENTS. ╘HESE HAVE THEIR S AND P LEVELS ONLY PARTIALLY FILLED AND EXHIBIT A VALANCE, OR CHARGE TO WHICH THEY EITHER GIVE OR GAIN ELECTRONS WHEN SHARING.
3. ╘HE TRANSITION METALS. ╘HESE ARE METASL WHICH HAVE THE S AND NEARBY D LEVEL FILLED WITH ELECTRONS. ╘HE TRANSITION ELEMENTS ARE GROUP B ELEMENTS.
4. ╘HE INNER TRANSITION METALS. ═ETALS WHICH FILL THEIR OUTERMOST S AND NEARBY F SUBLEVELS WITH ELECTRONS ARE CALLED THE INNER TRANSITION METALS. ┬OTH THE ╠ANTHANIDES AND THE ┴CTINIDES ARE CONSIDERED INNER TRANSITION METALS SERIES.
╘HE ELEMENTS OF GROUP 1A ARE CALLED THE ┴LKALI ═ETALS. ╘HEY HAVE LOW DENSITY, MELTING POINTS, AND GOOD CONDUCTIVITY. ╫HEN CUT WITH A KNIFE, THEIR SURFACE IS SHINY, BUT QUICKLY DULLS WHEN EXPOSED TO AIR DUE TO INTERACTIONS WITH AIR AND MOISTURE. ╘HESE ELEMENTS ARE NOT FOUND IN THE ELEMENTAL STATE IN NATURE. ╘HEY REACT VIGOROUSLY WITH WATER, PRODUCING OXYGEN AND A METAL HYDROXIDE, WHICH IS ALKALINE. ┼LEMENTS OF THIS GROUP INCLUDE HYDROGEN, LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CESIUM, AND FRANCIUM, ALTHOUGH HYDROGEN IS OFTEN PUT IN A CLASS ON ITS OWN, BEING A GAS.
╘HE ELEMENTS OF GROUP 2A ARE CALLED THE ┴LKALINE ┼ARTH ═ETALS. ╔N REACTIONS WITH WATER, THEY PRODUCE ALKALINE SOLUTIONS. ╘HEY ALSO ARE NOT FOUND IN ELEMENTAL STATES IN NATURE, BUT ARE LESS REACTIVE THAN THE ┴LKALI ═ETALS. ╘HEY ALL HAVE A GREY-WHITE LUSTER BUT ALSO TARNISH QUICKLY IN AIR. ┼LEMENTS OF THIS GROUP ARE BERYLLIUM, MAGNESIUM, CALCIUM, STRONTIUM, BARIUM, AND RADIUM.
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½└└█└└█└└█└└█└└█└└█└└█└└█└└█└└│ ╔NNER ╘RANSITION
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╘HE TRANSITION SERIES OF ELEMENTS ARE LIKE THE REPRESENTATIVE ELEMENTS AND THEY ARE THEREFORE BROKEN DOWN INTO GROUPS. ╙TARTING FROM THE LEFT ARE GROUPS 3B-7B, HEADED BY THE ELEMENTS SCANDIUM, TITANIUM, VANADIUM, CHROMIUM, AND MANGANESE. ╬EXT COMES GROUP 8B, OR MORE COMMONLY CALLED THE 'IRON GROUP.' ╘HIS GROUP IS HEADED BY THE THREE ELEMENTS ARE IRON, COBALT, AND NICKEL. ╘HIS GROUP IS FOLLOWED BY GROUPS 1B AND 2B, HEADED BY COPPER AND ZINC RESPECTIVELY.
╘HE INNER TRANSITION ELEMENTS FALL UNDER NO PARTICULAR GROUP SINCE THEY ARE OF TWO SERIES, THE LANTHANIDE (PERIOD 6) AND THE ACTINIDE (PERIOD 7). ╨ERIOD 7 CAN ALSO BE BROKEN DOWN INTO ACTINIDES AND TRANSURANIUM ELEMENTS. ┬OTH THE TRANSITION AND THE INNER TRANSITION METALS ARE TYPICAL METALS. ╘HEY ARE GOOD CONDUCTORS OF HEAT AND ELECTRICITY AND HAVE METALLIC LUSTER.
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▌ ▌ ▌ ▌ ╘HE ├HALCOGENS,
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╘HE CHALCOGENS ARE THE ELEMENTS OF GROUP ╓╔ OF THE ╨ERIODIC ╘ABLE--OXYGEN, SULFUR, SELENIUM, TELLURIUM, AND POLONIUM. ╘HE NAME IS DERIVED FROM TWO ╟REEK WORDS MEANING "COPPER" AND "BORN," BECAUSE MOST COPPER ORES ARE PRINCIPALLY COMPOUNDS CONTAINING OXYGEN AND SULFUR, WITH SMALL AMOUNTS OF SELENIUM AND TELLERIUM ALSO PRESENT. ╨OLONIUM IS A RARE, RADIOACTIVE ELEMENT THAT IS NOT ALWAYS INCLUDED AMONG THE CHALCOGENS. ┴S IS TYPICAL OF THE MAIN GROUP ELEMENTS, THE CHALCOGENS EXHIBIT TRENDS IN THEIR PROPERTIES WITH INCREASING ATOMIC NUMBER. ╘HE LIGHTEST MEMBER, OXYGEN, HAS PHYSICAL AND CHEMICAL PROPERTIES THAT ARE MARKEDLY DIFFERENT FROM THOSE OF THE HEAVIER MEMBERS. ╞OR EXAMPLE, ELEMENTAL OXYGEN AND SULFUR, IN THEIR PROPERTIES, SHOW NO RESEMBLANCE TO METALS, WHEREAS SELENIUM AND TELLURIUM ARE ELECTRICAL CONDUCTORS WHEN EXPOSED TO LIGHT, AND POLONIUM IS A METALLIC CONDUCTOR.
╘HE HALOGENS ARE GROUP 7A ON THE ╨ERIODIC ╘ABLE, CHLORINE, FLUORINE, BROMINE, IODINE, AND ASTATINE ARE A PART OF THIS GROUP. ╘HE NAME HALOGEN COMES FROM THE GREEK WORDS "HALOS" AND "GENS" ROUGHLY MEANING "SALT-BORN." ┬ECAUSE OF THEIR SIMILAR ODORS, ELECTRON CONFIGURATIONS, AND COMMON VALENCE CHARGES, THEY ARE PLAVED IN THE SAME GROUP. ╘HE FIRST TWO ARE GASES WHICH REACT WITH METALS TO FORM SALTS. ╘HE MOST COMMON OF THESE IS ╙ODIUM ├HLORIDE (╬A├L) WHICH FORMS BETWEEN ELEMENTAL SODIUM AND CHLORINE GAS. ╘HERE ARE ALSO SALTS OF IODINE AND BROMINE, AS WELL AS STRONG ACIDS LIKE ╚YDROFLUORIC AND ╚YDROCHLROIC ACIDS. ╚ALOGENS DO NOT EXIST IN THEIR ELEMENTAL STATES IN NATURE, BUT ARE FOUND ABUNDANTLY IN COMPOUNDS.
╚ELIUM, ARGON, KRYPTON, NEON, RADON, AND XENON ARE ALL MEMBERS OF THE NOBLE GAS GROUP, NUMBER 0 ON THE ╨ERIODIC ╘ABLE. ╘HE ORIGINAL NAME, RARE GASES, CAME ABOUT BECAUSE THESE SIX OCCUR ONLY IN MINUTE AMOUNTS IN THE ATMOSPHERE. ┼ARLY CHEMISTS CALLED THESE GASES INERT GAS BECAUSE THEY DID NOT KNOW OF ANY COMPOUNDS FORMED WITH THEM. ╬OW, AFTER THE DISCOVERY OF SEVERAL COMPOUNDS OF THESE ELEMENTS, NOT THE LEAST OF WHICH BEING ╪E╞4, THE NAME HAS BEEN CHANGED TO ╬OBLE GASES BECAUSE THEY PREFER THE 'NOBILITY' OF BEING APART FROM THE OTHER ELEMENTS. ┼ACH OF THE NOBLE GASES HAS ITS OUTERMOST ORBITAL COMPLETELY FILLED.
